I'm a science journalist and author of "Distant Wanderers: the Search for Planets Beyond the Solar System" who writes about over-the-horizon technology, primarily astronomy and space science. I’m a former Hong Kong bureau chief for Aviation Week & Space Technology magazine and former Paris-based technology correspondent for the Financial Times newspaper who has reported from six continents. A 1998 winner in the Royal Aeronautical Society's Aerospace Journalist of the Year Awards (AJOYA), I’ve interviewed Nobel Prize winners and written about everything from potato blight to dark energy. Previously, I was a film and arts correspondent in New York and Europe, primarily for newspaper outlets like the International Herald Tribune, the Boston Globe and Canada's Globe & Mail. Recently, I've contributed to Scientific American.com, Nature News, Physics World, and Yale Environment 360.com. I'm a current contributor to Astronomy and Sky & Telescope and a correspondent for Renewable Energy World. Twitter @bdorminey

Artist's concept of the X-43A Hypersonic Experimental Vehicle, or "Hyper-X" in flight. The X-43A was developed to flight test a dual-mode ramjet/scramjet propulsion system at speeds from Mach 7 up to Mach 10. (Photo credit: Wikipedia)

Like some hypersonic carrot, the idea of breakfast in Paris; breakfast again in New York; then late night cocktails in Tokyo — all within the same 12 hour workday — has been dangled in front of the flying public for so long now that any mention of Mach 7 aircraft may trigger involuntary eye-rolls.

Hypersonics using rocket propulsion is a staple of the space age, but hypersonics using air-breathing aircraft engines is something altogether more challenging.

Such technology involves aircraft designed to traverse the atmosphere at speeds at least 5 times that of sound — (3300 mph at altitude).

The key to making it happen are scramjets (supersonic combustion ramjet engines), which allow for supersonic airflow through the engine’s combustion chamber. That’s a feat currently not possible or advisable on commercial turbofan engines — like those used on most commercial airliners.

Although scramjets were first conceptualized in the 1950s, no one has yet achieved the development of a sustainable and reliable hypersonic aircraft propulsion system.

But, to date, NASA currently holds the world jet-powered speed record for its X-43A experimental aircraft which hit Mach 9.68 on November 16, 2004.

For perspective, Forbes.com turned to James Pittman, an aerospace engineer and Senior Advisor for the Fundamental Aeronautics Program, at NASA Langley Research Center in Virginia.

What is hypersonics biggest hurdle?

The critical challenge is the aero-heating, caused by the friction of air rushing over the vehicle’s solid surface at extreme speeds. Aero-heating dominates every aspect of hypersonic vehicle design: materials, vehicle shape, and internal heat management. It’s generally not a significant problem at speeds less than or equal to mach 2. But at hypersonic speeds [aero-heating] can cause extremely dangerous temperatures of up to two to three thousand degrees Fahrenheit. That can melt aluminum and titanium. Temperatures like that are a threat to the vehicle and anything inside it. Is there any technology on the horizon that could solve this heat problem?

Ceramic matrix composites could take those temperatures. Manufacturers are looking into developing these composite materials to integrate into a turbine engine’s core. But General Electric is probably the industry leader in investigating these matrix composites’ use in conventional turbine [aircraft] engines. What about the U.S. military’s own involvement in the development of hypersonic aircraft?

The Air Force and DARPA (Defense Advanced Research Projects Agency) are following along with a similar configuration called the X-51A. They have had three attempts. One [test] got 143 seconds of scramjet power. But the second and third flights did not achieve scramjet combustion. But the U.S. Air Force is leading the way in terms of developing scramjet technology in this country.

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Mass transit as hypersonic speeds should be possible with mag-lev trains in evacuated tunnels. If it were up to me, that’s where I would fund the R&D rather than hypersonic aircraft. The latter, however, will get more attention because it has military applications.

Hypersonic commercial flights via scramjet technology may well be decades away. I suggest that the author looks up the Sabre engine concept currently under mid-stage development by Reaction Engines Ltd. in the U.K. I believe that this technology will overtake scramjet.

Rather an omission given that the Sabre engine solves many of the so-called hurdles mentioned above. I wonder if there is a problem with science and engineering these days where too many experts are too deep into their own narrow field and could benefit from some wider knowledge, even if that wider knowledge is less deep.

Pittman had no specific comment on this development. But I thank you for your raising the issue. Pittman says that as a NASA employee, he normally doesn’t comment on specific private commercial ventures or activities of foreign governments.